Preparation of leucine



Patented July 27, 1948 UNITED rsrArEs East Greenbush, N.

-e assi nq 'sr w mesne assignments, .to winthrop stearns Inc.,. N,ew York, N. Y., a corporation.,ofpelaware No Drawing. Application september '22 l944,

. Serial No. 555,403

4 Claims. -(c tzso 4sz) This invention relates to a process for the preparation of alpha-amino acids,;and;to inter- 1.1. mediates for the preparationthereof.

Themalonic ester synthesis ,previously, has been adapted to the preparation of a number of alpha-amino acids, among these being leucine, isoleucine, norleucine, methionine, phenylalanine, valine, histidine, proline, and lysine. A useful modification of this method involves condensing an alkyl or aralkylhalide with. the sodio derivativeof an ethyl acylaminomalonate and then hydrolyzingland decarboxylating the condensation product to yield the amino acid. The ethyl acylaminomalonates which previously have. been used in this process are aromatic compounds, namely ethyl phthalimidomalonate [Sorenson Zeit.

Physiol.'Chem., 44, 448-460 (1905)] and ethyl b-enzamidomalonate [Redemann and Dunn, J. Biol. Chem, 130, 341-348 (1939)].

.When, however, thislmethod is utilized for-the .preparation of aliphatic amino acids. certain drawbacks are encountered. For example, many of the requisite saturated alkyl halidesare relatively difiicult to obtain pure.

We have found that these drawbacks can be r overcome by using, instead of thesaturated, alkyl w halides, the fi,Y-unsaturated halides, and subsequently reducing the double bond in the condensation product. This procedure, although at first sight longer in involving an additional step, has many advantages. In contrast to the saturated alkyl halides, the requisite unsaturated halides 1 in many instances can more readily be obtained pure, andhence aremuch cheaper. I Moreover,

they react with much greater facility.

such as an alkyl acylaminoma-lonate, catalytically reducing the condensation product, and hydrolyzing and decarboxylating the reduction product to yield an alpha-amino acid. The reactions involved in our process can be represented by the f allowing equations: 4

Ra Ra C 0-K: (1] a} 1 condensing R1- GHz-ha1ogen H-C-OOO.R4 i agen acylamino R 1 R a d 3?, T-P l dr an alkyl group and R4 represents. an alkylf group. ,.alk lacylam nome oh b i r apre r. o m l x a r aliphatiaabiflmim 5 ;,deriyatiye. '1 for example, the useofethylacetylaminomalonatehas aldeiinite 1 advantageovr the use of the, corresponding ,phthal'oyl and benzoyl 1; compounds, in that the subsequent removal'of the acetyl group in the process leads to thefclrmation of acetic acid rather than phthalic or ,benz'zoic acid. These latter acids bjein Solids, require additional purification steps to remove them from :ihe. ralnhaeam n ac d. n 1 1=c r i ce acid, which, being avolati-le, water-soluble liquid, cantbe quite simp y, separat d f om. the es r product.

@The catalytic reduction 7 can be, conveniently carriedv out-,byl treatment with hydrogen at 2-3 atmospheres inthe presence of a nickel, catalyst, .suchas; Raney nickel; The hydrolysis and, de- .carboxylation steps can be effected, simultaneously byl refluxing thereductionproduct with mineral acid, preferably. concentrated hydro- 'bromic acid. l -In..its broader aspects our.invention. compre- .-hends condensing fa A?-alkenyl,halide with a com -pound having the formula 4 where M represents one equivalent of a member of the class consisting c t -alkali and alkaline earth met ls a d A i e rh e y l or l a and converting the, resulting compound. into an alpha- Q ami o ac dbv apprcn en hydrolysis andreduction stepsl -When A is carbalkoxy, th e process can be conducted satisfactorily re ard ess. Q it b 1 6 QUhe hydrdlys a m' uct qn ste s alth u h it is .pr r'k to u m the condensation productprior to lriydrolysis.- If, 4 however, Aisacyl or lcyano, sincethese groups ,arethemselves suscept b e 150 d1 i m 3 desirable mixture of products frequently results if the; hydrogenation is conductedfprior"tore- ,moval of .these groups hydrolysis." For this .f..,r, as n,t e gr ups a e .r bv 5 Ih ro1ys1s prior to carryingbutthe reduction.

Eh p l rv axam HStI WQQIiDYwtion without, however, 11 ngsifitheretd catalyst in vacuo.

Example 1 Five and nine-tenths grams vof 3-chloro-2- methyl-propene are added dropwise with stirring to a solution of 10.9 g. of ethyl acetylaminomalohate in 100 ml. of anhydrous ethanol to which 1.15 g. of sodium have been added and the mixture is then refluxed for six hours. The alcohol is removed in vacuo and to the pale yellow residue are added 25 ml. of water and 25 ml. 'of chloro- :form. The water layer is separated and is ex- 2 acetylamino 2 carbethoxypentanoate placed in 8 ml. of 48% hydrobromic acid solution tracted with a ml. and a 10 ml. portion of chloroform. The chloroform extracts are combined and the chloroform removed by distilla--- nickel is added. The mixture'is treated with hydrogen 'under approximately 40 pounds pressure at room temperature for twenty minutes. The catalyst is then removed by filtration and the alcohol is removed by distillation. The residue, which is ethyl 2-acetylamino-2-carbethoxy- 4-methylpentanoate,weighs approximately 10.7 g. The compound melts at approximately 84 C.

To 5.46 g. of ethyl 2-acetylamino-2-carbethoxy- 4-methylpentanoate are added 16 ml. of 48% hydrobromic acid and the solution is refluxed for seven hours. The solution is then boiled with charcoal, cooled and filtered. The filtrate is adjusted to'pH 6 by the addition of concentrated ammonia water. The mixture is coole'd'for sev eral hours and the precipitate which forms is collected on a filter. "Five milliliters of water are added to the solid and then 5 mlyof ethanol. The mixture is cooled and the insoluble material is collected on a filter. The solid weighs 2.10 g. The product, which is dl-leucine, decomposes at approximately 278283 C'. It forms an N-ben- ,zoyl derivative which melts at 138-141 C.

ExampZcZ Fifteen and seven-tenths grams of allyl bromt'ide are added dropwise with stirring to a solution of 21.7 g. of ethyl acetylaminomalonate in I 1200 ml. of anhydrous ethanol to which 2.3 g. of

sodium have been added. The solution is refluxed ifior six hours and the alcohol is thenremoved To the residue are added 40 ml. of water and 50 m1. of chloroform. The water layer is separated and is extracted with a 40 ml. and

the solution is filtered.

of pyridine. gram.

and the mixture is refluxed for nine hours. The solution is then boiled with charcoal, filtered and the'filtrate evaporated to dryness. The residue is treated with 5 ml. of anhydrous ethanol and The product, norvaline, is precipitated from the filtrate by the. addition The yield is approximately 0.31 The hydrochloride decomposes at 184- 188 C. In the following claims the term lower fatty acy denotes a group derived from a lower fatty acid by removal of OI-I from the carboxyl group.

We claim:

1. The process for preparing dl-leucine which comprises condensing a methallyl halide with a compound having the formula alkali metal O (O O O-a1ky1)z lower fatty acyl-NH- wherein the lower fatty acyl group is derived from a volatile, water-soluble lower fatty acid by removal of OH from the carboxyl group, hydrogenating the condensation product and hydrolyzing and decarboxylating the hydrogenation product by heating it with strong mineral acid.

2. The process for preparing. dl-leucine which comprises condensing methallyl chloride with ethyl acetamido'sodiomalonate, hydrogenating the condensation product and hydrolyzing and decarboxylating the hydrogenation product by heating it with concentrated hydrobromic acid The catalyst is removed by filtration and the alcohol is re ,moved from the filtrate by distillation. The re- '75"France (4), vol. 43, pages 932-933.)

solution.

3. Ethyl 2 acetylamino 2 carbethoxy 4 methyl-4-pentenoate.

4. The process for preparing dl-leucinewhich comprisescondensing a methallyl halide with a compound having the formula alkali metal o (o o oalkyD'z' acetyl-NH i V hydrogenating the condensation product and hydrolyzing and decarboxylating the hydrogenation product by heating itwith strong mineral acid.

' SYDNEY ARCHER.

NOEL F. ALBERTSON.

REFERENCES CITED The following references are file of this patent:

UNITED STATES PATENTS of record in the Number Name 7 Date 7 1,239,867 Blagden Sept. 11,1917 1,844,394 Jaeger Feb. 9, 1932 Schmidt et a1 July 25, 1939 OTHER REFERENCES Karrer et al.: Helv. Chim. Acta., vol. '18 (1935) pages 782, 783, 783.

Sorenson: Zeit. Physiol. Chem., vol. 44, pages 448-460 '(1905).

Redemann et al.: Jour. Biol. Chem, vol. 130, pages 341-348 (1939).

Locquin et al.: Beilstein, vol. 4, 2nd suppl, pages (Abstract of Bull. Soc. Chim. de 

